Conventional marine speedometers have traditionally been based upon the use of pitot tubes, which are secured to the craft in a manner such that the pitot tube is drawn through the water as the craft moves, thereby creating an impact pressure which is utilized to pneumatically actuate a speedometer of a type comprising in effect a species of mechanical gauge. Examples of typical preferred such pitot tubes are shown in commonly-owned prior U.S. Pat. Nos. 3,181,356 and 4,070,909, which are incorporated herein by reference.
While such conventionally-known types of marine speedometers are generally reliable devices which are in many common applications reasonably acceptable, there are a number of instances in which it would be desirable to utilize electrically-actuated meter movements or displays in order to implement more advanced formed of instrumentation as marine speedometers. This development has for the most part been precluded heretofore, however, largely because appropriate velocity sensors or pickups for such applications have not been discovered by the marine industry, apart from a paddle wheel-type device which has a very limited range of application, principally being suitable for use at only very low velocities and, in particular, on marine craft with non-planing hull designs. Accordingly, there has until now been little or nothing of a commercial nature in electrically-operated marine speedometers which are suitable to ski boats, racing hulls, and a wide variety of analogous pleasure boats.
The aforementioned gap in the development of modern speedometer instrumentation for marine craft has been increasingly acute in relation to modern automotive speedometer instrumentation development, for example, in which a number of electrically-operated instruments have been developed with strikingly contemporary and innovative characteristics, e.g., digital speedometers and sweep-type or moving-field liquid crystal display devices. As will be appreciated, these types of speedometers are usually perceived by speed enthusiasts as being exciting developments which are equally desirable in marine craft, particularly in those boats which are utilized in speed-oriented recreational activities such as those noted above. Nonetheless, until the advent of the present invention no reliable and proven system was available by which such new instrumentation trends could be utilized in marine craft and in fact electrically-actuated marine speedometers in and of themselves have been encountered only on a very infrequent basis compared to the typical and customary pitot tube-impact pressure speedometer system.